1. Field of the Invention
The present invention relates generally to the field of wireless communications, and specifically to the use of radio frequency transmissions to track the movement of commercial goods, as well as other suitable applications.
2. Description of the Related Art
Consumers are familiar with electronic systems for recognizing, tabulating, and indexing the movement of goods through the chain of commerce. Everyday examples include bar codes combined with optical scanners as found in a supermarket. More recently, some products and their containers have been “tagged” with radio frequency identification (RFID) transponders, which in combination with a radio frequency reader and sophisticated computer systems, enable a commercial enterprise to track inventory from a distance. An RFID system includes a tag, a reader, and a computer network connected to the reader for compiling the relevant data.
RFID tags generally consist of a substrate material in which an antenna is located for receiving and transmitting radio signals. The antenna is connected to a silicon chip, or die, which is encoded with data concerning the object to which the tag is attached. The die itself can be of several varieties, including read-only memory (ROM), electronically programmable read-only memory (EPROM), and electronically erasable programmable read-only memory (EEPROM). Depending on the type of die used, a tag may be able to store data, transmit data to the reader, and be reprogrammed to adapt to new data inputs.
RFID tags come in two forms: active and passive. An active tag includes a power supply, such as a battery, that provides enough current to actively transmit the necessary data from the RFID antenna to a distal receiver. A passive tag is generally smaller than an active tag, and it does not include an independent power source. Rather, a passive tag derives its power from incoming radiation, such as that from an inquiring reader. Due to the advantageous size, weight, and cost of a passive tag, they are generally considered superior to active tags for use with highly mobile retail items and containers, including, for example, books and shipping boxes.
In spite of the advantages of the passive tag, there are numerous problems encountered with their maintenance, operation, and manufacture. In particular, given the sheer volume of commerce and the potential market for RFID tags, there are currently severe limitations in the manufacturing process that hinder the mass production of suitable tags.
In the manufacture of an RFID tag, the silicon die must be precisely placed and connected to the antenna. The placement of the die is generally done through robotics via optical alignment, at which time the bonds between the die and the antenna must be formed. Once the antenna is bonded to the die, the bond is cured. The curing process typically involves heat or ultraviolet (UV) radiation that interacts with a chemical photoinitiator in the bonding agent, thereby accelerating the hardening process. In a typical process, an epoxy containing a UV sensitive photoinitiator is used to bond the die to the antenna. The UV radiation then illuminates the bond site with sufficient fluence of photons of approximately 3 electron volts (eV) energy, and after several seconds, the epoxy hardens and the bond is formed.
The process outlined above presents a number of complications that hinder the large-scale production of RFID tags. First, as the economic demand for RFID tags reaches into the billions of units per year, the 8-10 second UV-curing process effectively limits the supply that manufacturers can theoretically muster. Secondly, once the die is bonded to the antenna, there is no simple method for removing the die if it fails to perform in the pre-shipment tests. Consequently, an estimated 20-40% of the RFID tags that fail the tests are irrevocably lost, further limiting the supply and increasing the cost of tags to businesses and consumers.
Given the foregoing, there is a need in the art for a reliable, cost-effective, and easily produced RFID tag that is usable over a range of commercial applications. Moreover, there is a need for a novel production method that is capable of large-scale cost effective production of RFID tags with reliable testing parameters and a high production yield.